Compositions of acrylonitrile polymers and ethylene oxalate and process for preparing same



Pat

Alfred B. Craig and Eugene L. Ringwald, Decatur, Ala., assignors to TheChemstrand Corporation, Decatur, Ala., a corporation of Delaware NDrawing. Application October 13, 1955 Serial No. 540,331

'7 lEC 7 Claims.

This invention relates to new compositions of matter and productsprepared therefrom. More particularly, the invention is concerned withthe production of new solutions of acrylonitrile polymers and to shapedarticles such as films, filaments, sheets, ribbons, tubes and the like,which can be formed from the new solutions.

This application is a continuation in part of our copending applicationSerial No. 279,250, filed March 28, 1952, now abandoned.

Polymers, as employed throughout the instant specification and claims,is intended to include polyacrylonitrile, copolymers and terpolymerscontaining at least 70% by weight in the polymer molecule ofacrylonitrile, and blends of polymeric acrylonitrile and copolymers ofacrylonitrile with polymers and copolymers of other polymerizablemono-olefinic monomers.

While the present invention is applicable to the preparation of variousshaped articles, such as are enumerated above, from polymericcompositions comprising acrylonitrile polymers, for purposes ofsimplicity of description the invention will be described as it isapplicable to the formation of fibers and filaments. It is to beunderstood, however, that this is merely intended in an illustrativesense and the invention is not to be limited thereby but only insofar asthe same may be limited by' the appended claims.

It is well known that acrylonitrile polymers have excellentfiber-forming properties. The conventional technique of fiberpreparation involves the dissolution of the polymer in a suitablesolvent, and thereafter extruding the solution into a medium whichremoves the solvent from the solution and precipitates the polymer incontinuous form. Heretofore, many known solvents have been employed todissolve acrylonitrile polymers for the purpose of forming shapedarticles therefrom. For example, various inorganic salts have beenemployed, such as zinc chloride, lithium bromide and the like. However,fibers spun by extrusion of aqueous salt solutions into coagulatingbaths which are non-solvents for the acrylonitrile polymers, usuallycontain large amounts of said salts. Fibers or other shaped articlescontaining these salts are not uniform and possess poor physicalproperties. Various organic solvents have also been employed for formingacrylonitrile polymer solutions, for the manufacture of shaped articles,such as fibers therefrom. However, many of these solvents are inferiorwith respect to solvent properties, or are too costly to provideeconomical fiber spinning conditions, or are too volatile or unstable atthe temperatures employed in normal spinning operations.

The primary object of the present invention is to provide a new solventfor acrylonitrile polymers which is unusually effective in dissolvingsuch polymers, and in addition, is economical and stable under normalspinning operations. Another object of the present invention is thepreparation of more stable solutions of acrylonitrile polymers which canbe readily formed into shaped articles. Another object of the presentinvention is to provide an improved method for preparing high tenacityfibers of 2,411,558 Patented July 1, 1858 ice Ethylene oxalate Thedispersion is then heated with stirring, tumbling, or other agitationuntil a free-flowing, uniform, homogeneous solution is obtained. Usuallyheating to a temperature within the range of 135 to 200 C. is suflicientto bring about complete dissolution of the polymer. The ethylene oxalatesolutions of acrylonitrile polymers are clear and homogeneous andreadily susceptible to being formed and/or drawn into fibers, films, andthe like by known and conventional procedures.

In the preferred practice of the invention the polymers of acrylonitrileare employed in a finely divided form. Although massive polymers may beground to desirable size, the selection of a suspension polymerizationprocedure, in accordance with the principles set out hereinafter, willproduce the desired subdivided state directly without resort to separatecomminution procedures.

The polymers which may be dissolved in ethylene oxalate to formsolutions for the production of shaped articles, as described herein,are polyacrylonitrile, co-

' polymers of acrylonitrile with minor proportions of othermono-olefinic compounds polymerizable therewith, and mixtures ofacrylonitrile polymers with other polymeric compositions, includingolefinic polymers or other types of polymeric substances. Thesemixtures, or blended polymeric compositions, are especially useful forthe purpose of developing dye-receptive polymers, for example byblending non-dyeable acrylonitrile polymers with a minor proportion of apolymer chemically reactive with dyestuff. In general, there is aminimum proportion of acrylonitrile which should be present in polymericform in order to have adequate tensile properties in the fibers preparedtherefrom. Thus, a polymer of monomeric mixture of which acrylonitrileis'at least of the polymerizable content, is useful in the practice ofthis invention. However, the solvent of the instant invention is capableof dissolving polymers of acrylonitrile containing any proportion ofacrylonitrile.

Useful copolymers, other than polyacrylonitrile, are

the copolymers of or more percent of acrylonitrile and e one or morepercent of other mono-olefinic monomers. Suitable other monomersinclude, vinyl acetate and other vinyl esters of monocarboxylic acids,vinylidene chloride, vinyl chloride and other vinyl halides, dimethylfumarate and other dialkyl esters of fumaric acid, dimethyl maleate andother dialkyl esters of maleic acid, methyl acrylate and other alkylesters of acrylic acid, styrene and other vinyl substituted aromatichydrocarbons, methyl methacrylate and other alkyl esters of methacrylicacid, methacrylonitrile, alpha-vinylpyridine and other vinyl substitutedheterocyclic nitrogen ring compounds, such as the vinyl imidazoles,etc., the alkyl substituted vinylpyridines, vinyl chloroacetate, allylchloroacetate, methallyl chloroacetate, allyl glycidyl ether, methallylglycidyl ether, allyl glycidyl phthalate and the corresponding esters ofother aliphatic and aromatic dicarboxylic acids, glycidyl acrylate,glycidyl methacrylate and other mono-olefinic monomers copolymerizablewith acrylonitrile. Of particular utility are the comonomers whichcontain one polymerizable olefinic radical whereby the copolymerizationwith acrylonitrile may be eifected and one acidic, basic or assures =3otherwise reactive group capable of bonding the dyestuff with which theultimate fiber may be treated.

Many of the more readily available comonorners for polymerization withacrylonitrile, form copolymers which are not reactive with the dyestuffsand may therefore be impossible or difiicult to dye by conventionaltechniques. Accordingly, these non-dyeable fiber-forming copolymers maybe blended with polymers or copolymers which are in themselves moredye-receptive by reason of their physical structure or by reason of thepresence of functional groups which are chemically reactive with thedyestutf, whereby the dyestufi is permanently bonded to the polymer in amanner which lends resistance to the usual laundering and dry-cleaningprocedures. Suitable blending polymers may be polyvinylpyridine,polymers of alkyl substituted vinylpyridine, polymers of other vinylsubstituted N-heterocyclic compounds, the copolymers of the variousvinyl substituted N-heterocyclic compounds and other copolymerizablemonomers, particularly acrylonitrile.

Of particular utility are the blends of non-dyeable acrylonitrilepolymers of good fiber-forming properties for example, polyacrylonitrileora copolymer of more than 90% acrylonitrile and up to 10% of vinylacetate, and a copolymer of vinylpyridine or an alkylsubstitutedvinylpyridine and acrylonitrile, the said acrylonitrile being present insubstantial proportions, for example 50 to 80% to provide heat andsolvent resistance, and a substantial proportion of the pyridine orderivative thereof to render the blend receptive to acid dyestuffs. Ofparticular utility are the blends of copolymers of 90 to 98%acrylonitrile and 2 to 10% vinyl acetate and sufficient copolymer of 10to 70% acrylonitrile and 30 to 90% vinylpyridine to produce a blendedcomposition with a total of 3 to 8% by Weight of vinylpyridine.

Other compositions suitable for blending with nondyeable acrylonitrilepolymers are: the polyamides prepared by condensing an alkylene diaminehaving up to six carbon atoms and a compound of the group consist ing ofcrotonic acid, acrylic acid, methacrylic acid and the alkyl esters ofthese acids, wherein the alkyl radical has up to five carbon atoms; thepolyamides prepared by condensing N-alkylazadinitriles withformaldehyde; the polyesters prepared by reacting dicarboxylic acidswith glycols containing tertiary amino groups; and other poly merscontaining tertiary amino radicals capable of reacting chemically withthe acid dyestuffs.

A further class of useful dye-receptive resins suitable for blendingwith the non-dye-receptive acrylonitrile polymers are the tertiary aminogroup containing polymers and copolymers described in the precedingparagraps which have been reacted with aliphatic halides, for examplebutyl bromide, chloroacetic acid, methyl chloroacetate, with the estersof oxygen containing sulfur acids, which ac ds have ionization constantsgreater than r6, methyl .9 and methyl p-tolucnesulfonate and with thevarious acids, such as sulfuric acid, hydrochloric acid andbenzenesulfonic acid. By these reactions blending resins containingamino groups are converted to quaternary or tertiary ammonium salts,-

which are more dye-receptive than are the corresponding amino groupcontaining resins.

Such polymers may be fabricated into fibers or films of unusualproperties, for example, high tensile strength, unusual thermal andchemical stability, and exceptional resistance to solvents. The optimumcombination of physical and chemical properties are found in thepolymers and copolymers of larger proportions of acrylonitrile, forexample in excess of 85%. It will be found that the practice of thisinvention with respect to the latter class of substances is mostbeneficial.

In the practice of this invention, as in the preparation ofacrylonitrile fibers by prior art methods, the physical properties ofthe polymers'are of substantial importance. It is desirable that thepolymers be uniform With respect to molecular Weight, particle size, andchemical composition. Accordingly, the methods for their preparationmust be selected so as to induce the uniformity of chemical and physicalproperties. In general, the molecular weight should be in excess of10,000 and preferably in excess of 25,000, the molecular weights beingdetermined by measuring the viscosity of dilute solutions in the mannerwell known in the art.

It has been found that polymers and copolymers of desirable physicalproperties are those which are prepared by the aqueous suspensiontechnique, wherein the monomers or mixture of monomers are added to anaqueous medium maintained under conditions suitable for a rapid butcontrolled polymerization. The aqueous medium should contain awater-soluble peroxy catalyst and a dispersing agent which induces theprecipitation of a finely divided polymer during the reaction. In orderto insure the optimum concentration of peroxy catalyst and dispersingagent it is frequently desirable to'add the catalyst and dispersingagent continuously or intermittently throughout the course of thereaction. The preferred practice involves the charging of the monomersor mixtures of monomers, gradually during the course of the reaction ata uniform rate or at a varying rate which permits the maintenance of thereaction at a constant temperature, for example the reflux temperature.

The fiber-forming acrylonitrile polymers are prepared by polymerizationin the presence of water-soluble peroxide catalysts, such as the alkalimetal salts of the various peroxy acids, for example sodium perborate,sodium percarbonate, and potassium persulfate, stabilizing or dispersingagents, such as the water-soluble salts of the sulfonated mahoganyacids, salts of the formaldehyde condensed naphthalene sulfonic acids,salts of sulfonaten alkylbenzenes, salts of triethanolamine, sodiumstearate and other salts of carboxylic acids, and mixtures thereofprepared by the sap'onifi'cation of animal and vegetable oils.

Desirable methods for the preparation of acrylonitrile polymers ofuniform molecular weight involve the use of regulators, for example,tertiary dodecyl mercaptan, beta-mercaptoethanol, thio-glycolic acid,beta-mercaptopropionic acid, and acetaldehyde. The nature of the othermonomeric substances being polymerized With the acrylonitrile maydetermine the type of substance useful as a regulator. For example, inthe copolymeriza= tion of acrylonitrile with monomers, such as vinylacetate, methyl methacrylate, and styrene, thioglycolic acid isunusually beneficial; However, in the preparation of copolymers of thebasic monomers, such as vinylpyridine, the use of tertiary aliphaticmer'captans will be found to be very effective.

t is desirable to use a solution of as high a concentration as possible,but the maximum concentration is dependent upon the molecular Weight ofthe polymer and the viscosity characteristics of the polymer-solventmixture. To obtain fibers of optimum physical properties polymers ofmolecular weights in excess of 25,000 are used, and with such polymersit is only possible to dissolve a relatively small proportion in theethylene oxalate without exceeding practical viscosity values. Althoughas little as 5% of polymer can be used in the spinning solution, suchlow concentrations are undesirable because they necessitate the removalof too much solvent from the extruded solution, thereby increasingsolvent recovery cost as well as reducing spinning speed and lengtheningthe period required for coagulation. The concentration of polymer in thespinning solution is usually between eight and 35 percent, butconcentrations up to the maximum are practicable. The concentration ofthe polymer will ultimately be determined by considering the desiredphysical properties of the fiber and the speed of spinning, the latterdepending upon the concentration and viscosity of the spinning solution.The viscosity will depend upon the'chemical composition and molecu-' larweight of the polymer, and the optimum concentration can best bedetermined by selecting a uniform high molecular Weight polymer havinggood fiber-forming properties, and dissolving a given amount in aslittle of the ethylene oxalate as possible to form a viscous solutioncapable of being spun at convenient temperatures.

The fibers are spun by extruding the polymer solution through anorifice, or a spinneret having a plurality of orifices, into a mediumwhich removes the ethylene oxalate. The volume of solution passedthrough the spinneret in a given time must be constant in order toproduce a fiber of a uniform size. This is 'best achieved by using apositively driven gear pump adapted to deliver a constant flow ofsolution regardless of minor changes in viscosity and the variableresistance offered by the spinneret. It is also desirable to pass thesolution, which has been prefiltered, through one or more additionalfilters before the spinneret to remove the last traces of foreign matterand particles of incompletely dissolved polymer. The polymers may bedelivered to the gear pump by pressures applied by an inert gas to thesolution reservoir, which is heated if necessary, to make the solutionfiuid enough to pass through the conduits. The extruding operationshould 'be operated at elevated temperatures, but well below the boilingpoint of the solvent to facilitate the handling of the apparatus.

The medium into which the solution is extruded and which removes thesolvent is preferably liquid. The method involving the use of liquids,known as wet spinning, usually utilizes water, alcohol, salt solutionsor any liquid which is a solvent for the ethylene oxalate, but in whichthe polymer is insoluble. The solvent is leached out of the stream ofpolymer solution which becomes a viscous stream and finally a solidfilament. When a spinneret with a plurality of apertures is employed,the several streams of polymer converged to form a single strand or tow.The spin bath must necessarily be of sufiicient size to permit thecomplete, or substantially complete, removal of the solvent. Obviously,the rapidity of extrusion will also affect the size of the spin bath,high speeds requiring longer baths. The temperature of the bath alsoaffects the size, higher temperatures permitting more rapid diffusion ofthe solvent out of the fiber and thereby permitting the use of shorterbaths.

In general, the methods of wet spinning which are in commercial use arereadily adaptable to spinning solutions of polymers in ethylene oxalate.Similarly, conventional automatic machinery for spinning continuously,drying the thread if necessary, and winding it upon suitable spools canbe used. As in the case of most synthetic fibers, those produced fromthe polymers of acrylonitrile, which are spun from ethylene oxalatesolutions, must be oriented by stretching to develop optimum physicalproperties. If desired, part of this stretching may be accomplished inthe spin bath, by drawing the fiber out of the bath more rapidly thanthe rate of extrusion.

Further details of the practice of the present invention are set forthwith respect to the following examples, which are merely intended to beillustrative and not limitative.

Example I Finely divided polyacrylonitrile (100%) was dispersed inethylene oxalate. The dispersion was then heated to approximately 180 C.with stirring. A clear homogeneous solution or dope containing solidswas obtained. Fibers were readily drawn from the ethylene oxalatesolution by conventional procedures.

Example II A finely divided copolymer containing 95% acrylonitrile and5% vinyl acetate by weight in the polymer molecule was dispersed inethylene oxalate. Thereafter the dispersion was heated to a temperatureof approximately 140 C. A clear homogeneous solution or dope containing10% solids was obtained. The resultant solution was then passed througha spinneret under pressure into a water bath and the fibers thus formedwere washed, dried, and steam-stretched for orientation. The fibers hadexcellent tensile and elongation properties.

Ethylene oxalate solutions of acrylonitrile polymers can also be castinto the form of films by passing the solution from a hopper onto arotating metallic surface under the smoothing action of a doctor blade.The solvent can be removed by any of the means well known in the art,for example, by a liquid bath containing a non-solvent for the polymer.In addition, molded articles can be prepared from the ethylene oxalatesolutions of the present invention. Further, the ethylene oxalatesolutions of acrylonitrile polymers as described in the instantinvention, may be employed as lacquers, coating materials, etc. Numerousother advantages of the present invention will be apparent to thoseskilled in the art.

It is to be understood that changes and variations may be made withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

We claim:

1. A new composition of matter comprising a homogeneous miscible mixtureof ethylene oxalate and a polymer of monomeric substances of whichacrylonitrile is at least of the polymerizable content.

2. A new composition of matter as defined in claim 1 wherein the polymeris polyacrylonitrile.

3. A new composition of matter as defined in claim 1 wherein the polymeris a copolymer containing by weight in polymerized form acrylonitrileand 5% vinyl acetate.

4. A new composition of matter as defined in claim 1 wherein the polymeris a copolymer containing by weight in polymerized form from 90 to 98%acrylonitrile and from 2 to 10% of a vinyl pyridine.

5. A new composition of matter as defined in claim 1 wherein the polymeris a blend comprising a binary interpolymer containing by weight inpolymerized form from 90 to 98% acrylonitrile and from 2 to 10% of vinylacetate, with a sufficient quantity of a binary interpolymer containingby weight in polymerized form from 10 to 70% of acrylonitrile and from30 to 90% of 2-vinylpyridine, to give an overall 2-vinylpyridine contentof 3 to 8% by weight.

6. A new composition of matter as defined in claim 1 wherein the polymeris a terpolymer containing by weight in polymerized form at least 2%vinyl acetate, from 90 to 94% of acrylonitrile, and from 4 to 8% of 2-methyl-S-vinylpyridine.

7. A process for preparing a fiber-forming solution comprising mixing apolymer of monomeric substances of which acrylonitrile is at least 70%of the polymerizable content with ethylene oxalate and then heating themixture to a temperature within the range of to 200 0.

References Cited in the file of this patent UNITED STATES PATENTS2,721,112 Downing et a1. Oct. 18, 1955 FOREIGN PATENTS 638,331 GreatBritain June 7, 1950

1. A NEW COMPOSITION OF MATTER COMPRISING A HOMOGENEOUS MISCIBLE MIXTUREOF ETHYLENE OXALATE AND A POLYMER OF MONOMERIC SUBSTANCES OF WHICHACRYLONITRILE IS AT LEAST 70% OF THE POLYMERIZABLE CONTENT.